Paving asphalt compositions

ABSTRACT

Asphalt compositions suitable for mixing with aggregate at high temperatures are produced by incorporating into an asphalt cement a minor amount, i.e., from 0.01 to 1.5 percent by weight, of a low-boiling hydrocarbon fraction. The resulting asphalt compositions have substantially improved compaction properties and are highly durable.

United States Patent Evans et al.

154] PAVING ASPHALT COMPOSITIONS [72] Inventors: Charles C. Evans,Concord; Harry J.

Summer, Lafayette, both of Calif.

[73] Assignee: Shell Oil Company, New York, NY.

[22] Filed: July 27, 1970 [21] Appl. No.: 58,690

[52] U.S. Cl ..106/278, 106/279, 106/280, 94/20, 94/23 [51] Int. Cl..C08h 13/00, C08h 17/22, C08i 1/46 [58] Field of Search ..106/273-285;94/19-22; 208/22, 23, 39

{56] References Cited UNITED STATES PATENTS 2,720,466 10/1955 Kalinowskiet a] 106/273 X [451 May 23, 1972 3,270,631 9/1966 Bower 106/277 X2,904,494 9/ 1 959 Grifi'm ..106/278 F ORElGN PATENTS OR APPLICATIONS608,711 11/1960 Canada 106/278 Primary Examiner.loan B. EvansAtt0rney-Glen R. Grunewald and John H. Colvin [5 7] ABSTRACT 8 Claims,No Drawings PAVING ASPHALT COMPOSITIONS This invention relates toimproved paving asphalt compositions. More particularly, it relates toasphalt compositions which when mixed with hot aggregate, produceasphalt mixes which are easily compacted and are highly durable.

Asphalt employed in paving applications must conform to a wide varietyof specifications including limits on penetration, viscosity,volatility, ductility, hardening on aging and the like. It is known thattwo asphalts whose initial properties meet specifications can behavedifferently after being subjected to mixing with aggregate at hightemperatures, e.g., temperatures of 250 F. or higher such as inconventional hot-mix plants. Although meeting all required specificationtests, the resulting asphalt-aggregate mix is in many cases difficult tocompact using conventional paving techniques and frequently, whencompacted, exhibits a tendency to shove under trafl'rc or scufi underthe action of power steering. Ease of compaction, while not normally aspecification requirement, is extremely important to contractors, sinceif the mix is too soft, rolling must be postponed until the mix coolsdown, or alternatively a better, more expensive aggregate must beemployed. Neither of these expedients is economically attractive to thecontractor and in some cases none of the locally available aggregatescorrect the deficiency.

It has become increasingly recognized in the art that the compactionproperties of an asphalt-aggregate mix are closely related to thepost-aging viscosity of asphalt, i.e., viscosity of the asphalt afterbeing subjected to an oven test under conditions simulating thehardening effect of hot mixing. Representative of such tests are theThin Film Oven Test (ASTM D 1754) and the Rolling Thin Film Oven Test(California Test Procedure 346-C). Asphalts which produce mixes havingdesirable compaction properties generally exhibit an increase inviscosity upon aging. For example, asphalts which have a post-aging topre-aging viscosity ratio at 140 F. of 2 to 3 or higher normally producemixes which are relatively easy to compact, while asphalts havingviscosity ratios of 1.5 to 2.0 generally produce mixes which are moredifi'rcult to compact, thus, necessitating longer periods of waitingbetween the spreading and compacting steps.

Although characteristics of asphalt which influence the compactabilityof the asphalt-aggregate mix are to some extent known, it is not alwayspossible to produce an asphalt having the desired properties because ofthe variety of crudes from which such products are manufactured, andcompeting economic factors such as the current emphasis on maximizingdistillate recovery. in order to maximize the distillate recovery,severe reduction of the asphalt-containing residue is necessary, forexample, by deep vacuum flashing or deep propane deasphalting. Suchtechniques result in the production of hard asphalt base stocks, whichalthough generally are very durable, would not meet grade specificationsfor paving asphalt. Thus, there is need in the art for asphaltcompositions, which in addition to meeting the many traditionalspecification requirements for paving grade asphalts, also produceasphalt-aggregate mixes having good compaction properties which are ofprime importance to contractors.

It has now been found that paving asphalt compositions suitable forproducing asphalt-aggregate mixes having improved compaction propertiescan be prepared by incorporating into an asphalt cement, a minor amount,e.g., 1.5%w or less, of a low-boiling hydrocarbon fraction having aboiling range of from about l F. to about 550 F. The asphaltcompositions of the invention are characterized as high flash pointasphalts, i.e., compositions having flash points of at least 440 F. andpreferably above 500 F., thus enabling them to be employed inapplications wherein the asphalt and aggregate are mixed at hightemperatures such as in a hot-mix plant.

The term asphalt cement as employed in the specification and claims, isdefined as any asphalt suitable for use in paving work and other asphaltmix construction. Blending components for asphalt cements includestraight-reduced asphalts, asphalts obtained by solvent fractionationsuch as propane asphalts, thermal asphalts, natural asphalts such asgilsonite,

and oils of high molecular weight. Asphalt cements typically havepenetration values of from 20 to 300 and can be brought to any desiredconsistency by mixing or fluxing with harder or softer components as thecase may be. Penetration numbers appearing in the specification unlessotherwise indicated refer to penetration values at 77 F. determined inaccordance with ASTM D 5 under a load of grams for 5 seconds.

Low-boiling hydrocarbon fractions suitable for incorporation into thepresent compositions are those having the boiling ranges hereinbeforespecified and include fractions commonly referred to as kerosene,mineral spirits, naphthas and the like. These fractions can beincorporated into the base asphalt in amounts of from 0.01 to 1.5percent by weight on the basis of the total composition. Asphaltcompositions containing from 0.5 to 1.0 percent by weight kerosene ormineral spirits, or from 0.3 to 0.8 percent naphthas have been found tobe particularly advantageous. The low-boiling hydrocarbon fraction maybe incorporated into the asphalt cement, in any convenient manner, forexample, added directly to the base asphalt, or blended with anotherasphalt first, and then added to the base asphalt. A very convenientmethod of addition is to add a measured quantity of a cutback asphalt ashereinafter defined to a base asphalt, thus producing an asphalt cementhaving the desired concentration of low boiling hydrocarbon material.

The incorporation of the low-boiling hydrocarbon fraction into the baseasphalt in the above-specified amounts, while appreciably improving thecompaction properties of the aggregate-asphalt mix has been found tohave minimum adverse effects on the flash point and other properties ofthe blend, and in some instances has brought about unexpectedimprovements. For example, long term durability in the road has beenfound to remain unaffected or may even be improved with asphaltscontaining small amounts of low boiling solvents. Measurement of thisdurability is best simulated by California Test Method 347-A whereinresidues from the Rolling Film Oven Test previously described aresubjected in thin films to further hardening in air at lowertemperatures for a longer period of time to simulate aging in the road.Viscosities of the durability residues are measured by means of thesliding plate microviscometer at 77 F. at two shear rates. The gooddurability of the present compositions as shown by the examples isparticularly surprising in view of US. Pat. No. 2,904,494 which teachesthat in order to obtain an asphalt product having good durability, it isnecessary that all fractions having a molecular weight below 400 beremoved.

Another unexpected feature of the present compositions is theirstability during prolonged periods of storage in tanks at relativelyhigh temperatures. Apparently because of the small amounts in which thelight hydrocarbon fraction is employed, this fraction becomes intimatelybound in the base asphalt and is not volatilized therefrom to any largeextent when stored at temperatures of about 300 F. or higher as wouldnormally be expected. 4

In addition, it has been found that the shear susceptibility of thepresent compositions containing the low-boiling hydrocarbons is actuallyimproved contrary to normal expectations as discussed in Example I.

The asphalt compositions of the invention are to be distinguished fromliquid asphalt products, also termed cutback asphalts, which areessentially solutions of bitumen in various solvents. Because suchcompositions are in liquid form, they can be applied directly to roadsurfaces, for example, by spraying, without having to be heated to hightemperatures prior to use. Cutback asphalts are employed for a varietyof purposes, e.g., surface treating of roads, cold-patching, asphaltpaints, etc., and generally are classified in three different types,i.e., rapid curing (RC), medium curing (MC), and slow curing (SC), therate of curing depending on the type and amount of solvent present. RCcutbacks are normally prepared using naphtha as solvent, whilekerosene-type diluents are used in MC cutbacks, and gas oils or otherheavier boiling fractions are employed in SC cutbacks. The amount ofsolvent varies somewhat depending on the grade, but generally rangesfrom 12 to 50 percent or higher. The specification requirements forflash point, viscosity, distillation range, etc., will also varydepending on the application for which the cutback asphalt is used. Forexample, MC cutbacks generally have flash points in the range 100 to 150F. and penetration values well above that measurable by the standardpenetration test. In contrast, the asphalt compositions of the inventioncontain very low concentrations of low-boiling hydrocarbons, haverelatively low penetration values and high flash points as hereinbeforediscussed.

The present invention will be further described by means of thefollowing examples which are given for illustrative purposes only,therefore, the invention in its broader aspects should not be limitedthereto. I

EXAMPLE I A base asphalt containing 2.25%w of MC-l, which in turncontains 32percent kerosene, was blended with a 200/300 penetrationvacuum residue as required to approach the extremes of the 85/100penetration grade. A conventional 85/ 100 penetration asphalt wasblended from similar base stocks produced from West Texas sour andOklahoma sweet crudes. Compositions and properties are recorded in TableI.

that viscosity to the viscosity after the rolling thin film oven test islower for Asphalt 1 and 2 than for the Conventional Asphalt. Thus, longterm hardening in the pavement can be expected to proceed at a lowerrate for asphalts prepared in accordance with the invention.

Shear susceptibility is the effect of shear rate on viscosity and isdefined as (log vis at 0.001 sec log vis at 0.05 sec) divided by log 50.Excessive shear susceptibility is considered detrimental to a pavementsability to relieve stresses due to changes in temperature and movementsof the subgrade. Although there are no specified limits at the presenttime, excessive shear susceptibility is known to lead to pavementfailure. From Table I, it is apparent that the new method of asphaltmanufacture not only gives mixes which are easier to compact butadditionally gives a binder with a lower shear susceptibility in servicethan the current asphalt. This is unexpected since low shearsusceptibility is usually associated with low viscosity ratios.

Conventional Asphalt Asphalt 3 sample time, B sample time,

months months Properties 0 0. 5 2. 5 4. 5 0 0. 5 2v 5 Penetration, tlmmS8 91 88 03 96 01 88 Flash, COC, 11. 505 565 605 600 505 605 630Viscosity, 140 F, poi 1,030 1,070 1,150 1,100 1,000 1,250 1,150 Thinfilm oven test:

Retained penetration, percent original 55. 7 51. 6 59 57 55. 2 52. 7 64.8

Viscosity of residue, 140 F., poises 3,160 3,170 2,090 2, 000 2,3502,800 2,425

Viscosity ratio 3.1 3.0 2. 6 2.6 2.3 2 2 2.1

TABLET" Asphalt Asphalt on 1 2 asphaltA Composition, percent w.:

Base asphalt 80. 6 73. 3 69. 5 200/300 penetration asphalt 17. 5 25. 030. 5 MC-l (containing 32% kerosene).. 1. 9 1. 7 Properties:

Penetration, dinm 85 97 93 Flash, COC, F. 610 620 640 Viscosity, 140 F.,p0 1,530 1,070 969 Thin film oven test (ASTM D 1754):

Weight loss, percent W 0.43 0.38 0.01 Retained penetration, percentorig- 5O inal 58 67 Viscosity of residue, 140 F., poise... 3, 900 2,8501,050 Viscosity ratio, residue/original. 2. 2. 7 2.0 Rolling thin filmoven test (RTFOT) California test procedure 346-0:

Retained penetration, percent original 54 58 62 Viscosity of residue,140 F., poise 5, 070 3,035 2, 220 55 Viscosity ratio, residue/original3. 3 2. 8 2. 3 Durability test on residue from RIIAOI California testprocedure 347- I Viscosity of residue, 77 F., megapoise:

Shear rate, 0.001 seer 67. 5 39. 5 38. 0 Shear rate, 0.05 sec.- 21. 912.6 11.0 Viscosity ratio, durability/RTFO'I:

Shear rate, 0.001 sec.- 13X10 13X10 17x10 Shear rate, 0.05 sec- 4x104X10 5X10 Shear susceptibility slope, 77 F. 0. 29 0. 29 0. 32

From the data in Table I it is evident that Asphalts 1 and 2, inaccordance with the invention, are substantially higher in postagingviscosity at 140 F. and in viscosity ratio than is the conventionalasphalt which is indicative of the superior compaction properties whichmay be expected from asphalt-aggregate mixes prepared from thecompositions of the invention.

The durability test which is run on the residue from the Rolling ThinFilm Oven Test is intended to simulate further aging in the pavementduring service. In this test a 20 micron film of asphalt is exposed toair for 24 hours in an oven at 210 F. While the viscosity after thedurability test is higher for Asphalt 1 and 2 than for ConventionalAsphalt A, the ratio of Frorn the foregoing results it is clearlyevident that the im- Conveni 40 proved post-aging viscosity andviscosity ratio of the inventive composition were substantiallymaintained during the period of storage.

EXAMPLE III To further illustrate the advantages of the presentcomposition, an asphalt cement comprising a hard base asphalt, and 1.3percent mineral spirits was prepared (Asphalt 4 shown in Table III), andits properties determined and compared to a conventional asphalt cementprepared from similar base stocks, but not in accordance with theinvention. The compositions of the respective asphalts and theirproperties are presented in Table III below. The asphalts described inTable III were derived from West Texas sweet crudes processed by deepvacuum flashing, air-blowing and blending.

TAB LE III Asphalt Conventional asphalt 0 Composition, percent w.:

Base asphalt, 2,100 poise at 140 F 08. 7 80.0 Soft vacuum flasherresidue 20. 0 Mincral spirits 1. 3 Properties:

Penetration, dmm 84 Flash, COO, F 580+ 640+ Viscosity. F., poise 1,1501,460 Rolling thin film oven test (RTFOT) California test procedure346-0:

Retained penetration, percent original Viscosity oircsidue, 140 F.,poise 3,350 2,500 Viscosity ratio, residue/original 2. 0 1. 7 Durabilitytest on residue from RTFOT California test procedure 347-A:

Viscosity of residue, 77 F., inegapoise:

Shear rate, 0.001 sec.- 12.0 9. 75 Shear rate, 0.05 seer 7. 5 3. 8Viscosity ratio, durability/R'IFOT:

Shear rate, 0.001sec.- 4X10 3 4X10 3 Shear rate, 0.05 secrL. 2X10 3 2X103 Shear susceptibility slope, 77 F 0.12 0. 24

From the results shown in Table 111 it is evident that Asphalt 4 of theinvention, containing the specified amount of mineral spirits, has asubstantially improved post-aging viscosity and viscosity ratio. Herethe viscosity ratios (viscosity of the residue from the durability testdivided by the viscosity of the residue from the RTFOT) were desirablylow in both cases showing the solvent in nowise degraded the durabilityfollowing the first aging step. While the shear susceptibility slope ofConventional Asphalt C is considered acceptable, this product has anundesirably low viscosity after oven aging. Asphalt 4 of the inventionhas both a very acceptable shear susceptibility slope and a desirablyhigh post-aging viscosity ratio.

The excellent compaction properties of asphalt-aggregate mixes preparedwith the present compositions have been observed in actual service inthe field. In one such test, 5,000 gal-- lons of Asphalt 3 was mixedwith aggregate at temperatures of 310 to 320 F. in a contractors hot mixplant and the asphalt aggregate mix applied to the surface of a parkinglot with highly satisfactory results.

We claim as our invention:

1. A paving asphalt composition having a flash point above 440 F. and apost-aging to pre-aging viscosity ratio of at least 2, consistingessentially of an asphalt cement having incorporated therein from 0.1 to1.5 percent by weight of a hydrocarbon fraction boiling within the rangeof from about F. to about 550 F.

2. The composition of claim 1 wherein the hydrocarbon fraction iskerosene.

3. The composition of claim 1 wherein the hydrocarbon fraction ismineral spirits.

4. The composition of claim 1 wherein the hydrocarbon fraction isnaphtha.

5. The composition of claim 2 wherein the hydrocarbon fraction isincorporated into the asphalt cement in an amount of from 0.5 to 1.0percent by weight.

6. The composition of claim 4 wherein the hydrocarbon fraction isincorporated into the asphalt cement by the addition of a rapid-curingcutback asphalt.

7. The composition of claim 2 wherein the hydrocarbon fraction isincorporated into the asphalt cement by the addition of a medium-curingcutback asphalt.

8. The composition of 4 wherein the hydrocarbon fraction is incorporatedinto the asphalt cement in an amount of from 0.3 to 0.8 percent byweight.

2. The composition of claim 1 wherein the hydrocarbon fraction iskerosene.
 3. The composition of claim 1 wherein the hydrocarbon fractionis mineral spirits.
 4. The composition of claim 1 wherein thehydrocarbon fraction is naphtha.
 5. The composition of claim 2 whereinthe hydrocarbon fraction is incorporated into the asphalt cement in anamount of from 0.5 to 1.0 percent by weight.
 6. The composition of claim4 wherein the hydrocarbon fraction is incorporated into the asphaltcement by the addition of a rapid-curing cutback asphalt.
 7. Thecomposition of claim 2 wherein the hydrocarbon fraction is incorporatedinto the asphalt cement by the addition of a medium-curing cutbackasphalt.
 8. The composition of 4 wherein the hydrocarbon fraction isincorporated into the asphalt cement in an amount of from 0.3 to 0.8percent by weight.